Document 13341

concentrations
of approximately
1 g/L
of urine, which are commonly
achieved
2 to 3 h after intravenous infusion, a
false-positive
result
for Bradshaw’s
test will occur.
We wish to alert clinical biochemists
and physicians to this source of interference, and stress the necessity of confinning. the validity
of all screening
tests for Bence Jones protein by measuring total urinary
protein
and using
specific electrophoretic and immunochemical tests to detect light chains in
fresh concentrated urine.
References
1. Johnson
phoresis
1797-1800
2.
AM. Immunofixation
electroClin Chem 28,
(1982).
and electrofocusing.
Gale DSJ, Versey JMB, Hobbs JR.
Rock-
et immunoselection for detection of heavychain diseases. Clin Chem 20, 1292-1294
(1974).
F.R.G.), for which the detection limit is
(2). In no case did we detect
immunoreactive material in undiluted
specimens. The absorbances at 492 urn
ranged from 0.020 to 0.040, no different
from that of blank incubations (0.020
0.6 g/L
to
0.035).
Similar
negative
were also obtained
fluids
results
for cerebrospinal
concentrated
fourfold
would surely
brane filtration. We conclude that, in
contradiction to the previous report (3),
immunoreactive PSG1 is either absent
from cerebrospinal fluid or is present
in concentrations definitely below 0.15
g/L. Because the sensitivity of the
enzyme immunoassay
(0.6 g/L) is at
least equal to or greater than that
reported for the radioimmunoassay
(1
g/L),
insensitivity
of the applied
method cannot be the reason for our
failure to confirm the presence of immunoreactive
PSG1 in human cerebro-
be reflected
ciency testing.
The introduction
handling
by mem-
exhibit
typical
of inter-lab s’ra.
sodium results in the area of 1.5 mmol.
A typical drift of 10 to 20 mniollL
in such profi-
into the sample-
system ofsodium,
potassium,
chloride, and calcium for an instrument designed to analyze these constituents may be somewhat risky. Sodium
drift of the magnitude reported is not
normal, and it is suggested that the
instrument in question be given a cbser look. Illegal grounding, salt bridges,
and static charges are possible offenders in a situation
like this.
Thomas
M. Happe
ASTRA
Applications
Beckman
Instruments,
Brea, CA 92621
Dept.
Inc.
Urine Urea Nitrogen
Astra-8
as Measured in
spinal fluid.
3. Bradshaw TR. The recognition
pathic albumin
in urine. Br Med
of myeloJ ii, 1442-
1444 (1960).
4. Hobbs JR. Bence-Jones proteins. Essays
MedBiochem
1, 105-131
(1975).
Peter Dennis
Beryl
Biegler
Ian Larmour’
Depts. ofChem.
Pathol. and ‘Pharmacy
Prince Henry’s Hospital
Melbourne,
3004, Australia
References
1. Bohn H, Schmidtberger R, Zilg H. Isolierung des schwangerschaftsspezifischen
f31-Glykoproteins
(SP1) und antigenverProteine
wandter
durch
Immunadsorption.
Blut 32, 103-113
(1976).
2. Dati F, Bauer 11W,Schuster E, Bartos
the Beckman
S.
Die
diagnostische
Relevanz
des schwangerschafts-spezifischen
/31-Glykoproteins
bei verschiedenen malignen Erkrankungen. J Clin Chem Clin Biochem 20, 651-652
(1982).
3. Heikinheimo M, Wahlstrom T, L.ehto
VP, et al. Pregnancy-specific $1-glycoprotein-like material in human cerebrospinal
fluid. J Clin Endocrinol Metab 55, 189-192
Questioning the Presence of
Pregnancy-Specific$1-Glycoprotein
(or Immunologically Similar
Material) in Cerebrospinal Fluid
(1982).
Axe! M. Gressner
Dept. ofClin. Chem.
RWTH
Klinikum
Aachen, F.R.G.
Pregnancy-specific
/31.glycoprotein
(PSG1), a high-molecular-mass
glycoprotein that normally is synthesized by
the syncytiotrophoblasts
during pregnancy, is increased
in serum
not only
in pregnancy but also in patients with
trophoblastic
and, less frequently,
with
non-trophoblastic
malignancies
(1, 2).
It is absent (<0.3 g/L) from the sera of
non-pregnant,
healthy
female
and
male subjects (2), but recently the presence of PSG1 in cerebrospinal
fluids of
men and women was reported (2). The
range of concentrations,
as determined
by radioimmunoassay
(detection limit
1 gfL), was 1.9 to 3.6 pg/L (3). A
correlation
with other factors or with
any specific cerebral diseases could not
be established.
We studied
PSG1 in 15 cerebrospinal fluid specimens, from children and
adult patients
with cerebral
tumors
and inflammatory
and ischemic
cerebral diseases. We used a solid-phase
enzyme-linked
immunoassay
(Enzygnost-SP1;Behringwerke AG, Marburg,
Sodium
Drift
ASTRA:
To the Editor:
The Letter of Seddon et al. (Clin.
29: 212, 1983) deserves cornment in the interest of all riu
users.
We agree with the authors that an
“upward
drift of 10 to 20 rnmol/L in
results for sodium” is not acceptable.
We disagree, however, that an ionic
wash solution provides an adequate fix
for the problem. The fact that a sodium
hypochionte
rinse (not a recommended
procedure)
will “temporarily
solve this
drift” suggests some type of containinaChem.
problem
before assay.
diluting
In the Beckman
in the sample-handling
system of the particular
In the Beckman Astra discrete analyzer, ion-selective electrode technology is used. The urea nitrogen method
in this system was designed for use at
conductivities
normally found for planma. When plasma samples contain
high, out-of-range
concentrations
of
urea nitrogen,
the samples routinely
are diluted
with physiological
saline
Because
A Response
tion
To the Editor:
the salt concentration
of
widely,
the question
of
urines with either physiologi-
urea varies
-
To the Editor:
1310
Chemistry
Survey,
standard deviations
instrument
cal saline or water before assay for
urea nitrogen becomes an important
issue with the Astra.
Blumenfeld and Griffith (1) exammed extensively
the Astra’s performance with urine Nat, K, C1, urea
nitrogen,
glucose, and creatinine, but
they did not comment on the preferred
diluent to use with a particular categoly of assay.
We have compared urine urea nitrogen as measured with the Astra-8 and
the American Monitor
KDA over a
wide range of concentrations
with isotonic saline as the diluent. In the KDA,
the enzymatic urease procedure is used
for urea nitrogen
analyses. Thirty patients’ samples, analyzed by both
methods, gave mean values that cornpared favorably (KDA = 87.39 nunol/L
vs Astra = 83.92 mrnolIL).
In our laboratory,
we routinely
di-
lute urine urea nitrogen samples with
involved.
physiological
proficiency-survey
programs, such as the College of Amencan Pathologists’
Comprehensive
inter-patient variability in urinary salt
concentrations. With this approach, we
have not experienced
the analytical
Ongoing
CLINICAL CHEMISTRY, Vol. 29, No. 6, 1983
saline
to minimize
the
fluctuations
in urine
urea nitrogn
re-
ported by other Astra users with this
method.
Reference
1. Blumenfeld TA, Griffith B. Measurement
of urinary
constituents
with
the
As-
tra-8 multi-channel analyzer. Clin Chem
26, 1883-1886
(1980).
cipitant),
successively decreasing volnines
of serum were added at room
temperature.
After their contents were
by the difficulty
mixed, the tubes stood for 15 mm before being centrifuged
at 4 #{176}C
for 30
mm. The cholesterol in each supernate
was measured with use ofan ABA-100
discrete analyzer and Bio-Dynamics/
cated to the kit manufacturer,
ElectroNucleonics, Inc. Their response pointed
out that the package insert in the kit
makes no claims about the total choles-
cholesterol
reagents.
The lipoprotein content of each supernate was monitored by agarose gel
electrophoresis
(5) to identify
the
ed out the recognized facts that the
results of HDL-C assays depend on
bmc
Laurence M. Demers
Brenda Dourte
Barbara Hutchinson
Dept. of Pat/wi.
The Milton S. Hershey Med. Center
The Pennsylvania
State Univ.
enzymatic
true”
Tube
no.
Evaluation of a Kit to Measure HDL
(HDL-C) in Serum
To the Editor:
A clinic laboratory got low values for
serum HDL-C on using a kit supplied
by Electro-Nucleomcs, Inc.’ In the kit,
the precipitating
reagents
(phosphotungstate and MgSO4) are supplied as
solids in a tube, to which 0.5 mL of
serum is added according to the manufacturer’s package insert.
We analyzed split human serum
samples in parallel with such kits and
using
our in-house phosphotungetate
method, a procedure like that of Lopes-
Virella
the pH
gent to
only 80
et al. (1), except that we adjust
of the phosphotungstate
7.4 or slightly
rea-
less (2), and add
plus 20
LL of MgCl2 reagents to 1.0 mL of
serum. Values obtained with the kit
were from 30 to 170 mg/L lower than
pL ofphosphotungstate
results with the in-house method, differences averaging 18.2% (SD 5.4%, n
= 16) for values ranging
from 280 to
1120 mg/L. Such differences would
cause many samples with total cholesterol/HDL-C
ratios near 5.3, based on
the in-house method, to have ratios
near 6.5 with the kit. These higher
ratios would imply an importantly
greater
risk of coronary
artery
value (the cholesterol
in the
supernate
disease
(3).
We further evaluated the kit by titrating
(4) three human serum sam-
ples with increasing ratios of precipitent to serum. To a series of kit tubes
(each contained the prepackaged pre-
Serum
vol, mL
Apparent
mg/L
HDL-C,
1
2
3
4
1.8
1.5
1.3
1.2
470
5
1.1
400
6
1.0
390
7
8
0.9
0.8
380
380
9
10
0.7
0.5
380
350
480
390
380
1 Use of products
from named companies
does not imply that the products are superior to similar products of comparable grade
from other companies, nor does it constitute
endorsement of the products by the United
Force.
such a
terolJHDL-C ratio. Further, they pointconditions and reagents and that there
were differences in both of these when
our phosphotungstate
reagents and
method
were compared
and the instructions
with
in the
their kit
package
insert.
References
1. Lopes-Virella MF, Stone P, Ellis S, Colwell JA. Cholesterol determination in highdensity lipoproteins separated by three different methods. Clin Chem 23, 882-884
(1977).
2. Grove TH. Effect of reagent pH on deterrnination
ofhigh-density lipoprotein cholesterol by precipitation with sodium phosphotungstate. Clin Chem 25, 560-564 (1979).
3. Uhl GS, Troxler RG, Hickman JR, Clark
D. Relation between high density lipoprotein cholesterol and coronary artery disease
in asymptomatic
men. Am J Cardiol 48,
903-910 (1981).
Because agarose gel electrophoresis
showed no LDL or VLDL in the supernates of tubes 3-10, the “true” HDL-C
concentration
appears to be 390 mg/L
(tubes 3-6). The HDL-C concentration
measured by our in-house phosphottmgstate method was 390 mgIL, while
the concentration measured with 0.5
mL of serum added to the kit tube was
350 mg/L. Similarly,
in the other two
titrations
also, the HDL-C values were
low when 0.5 mL of serum was added
to the kit tube. With 1.0 mL per tube,
however, agreement was satisfactory.
The clinic laboratory
then split a
group of serum samples, measured the
HDL-C
in one aliquot with use of 1.0
mL of serum per kit tube, and sent us
the other aliquot for analysis by our inhouse method. All values measured at
the clinic with the kit were 10 to 40
mg/L lower than our values, which.
ranged
from 260 to 630 mg/L. The
differences between the methods averaged 5.8% (SD 3.2%, n = 8). Although
these differences were statistically
significant, they were deemed acceptable
because they were small and
ent. Compared
with the earlier
States Air
from
which all VLDL and HDL had been
removed by precipitation
without detectable loss of HDL). Results from one
serum were as follows:
Hershey, PA 17033
Cholesterol
HDL-C
concentration
in measuring
volume.
The above findings were communi-
consist-
differ-
ences when 0.5 mL per tube was used,
the improvement
is obvious. Data from
the other titrations suggest that a serum volume slightly less than 1 .0 mL
(e.g., 0.85 mL) would be optimal, but
the gain in accuracy is apt to be offset
4. Clark DA, Wood JA. Titration of serum
lipoproteins with lipoprotein precipitants.
USAF School of Aerospace Med., Technical
Report SAM-TR-81-31,
Brooks Air Force
Base, TX 78235, 1981.
5. Noble RP, Hatch VF, Mazrimas JA, et al.
Comparison of lipoprotein analysis by agarose gel and paper electrophoresis with analytical ultracentrifugation.
Lipini 4, 55-59
(1969).
Dale A. Clark
R. Rozell
E. L. Mosser
Phillip
Clin. Sci. Div.
USAY School ofAerospace
Med.
Brooks Air Force Base, TX 78235
Cefoxitin Interference with Urinary
17-Hydroxycorticosteroid
Determination
To the Editor:
Because of the marked minute-tominute
variation in plasma cortisol
concentrations,
urine or total
either free cortisol in
17-hydroxycorticoster-
oids (17-OHCS)
excretion is the best
index to steroid output. The normal
response to dexamethasone has been
better established for urinary
17OHCS than for free cortisol (1); thus,
accurate determination of urinary 17OHCS is essential.
With the large increase in the num-
ber ofpharmacological
agents in recent
CLINICAL CHEMISTRY, Vol. 29, No. 6, 1983 1311